The most basic part of a biodiesel processor is the tank. These tanks can be made from a variety of materials and this article will discuss several different options.

Your tank needs a few different things:

Space: You have to have enough space for each batch that you make. Determine the ammount of oil you want to convert to biodiesel (for example 200 liters), make sure there is room for your methoxide (20 percent by volume of 200 liters is 40 liters) and leave a little room for mixing to take place (10 percent is a good number to shoot for, although it depends on your processor.) Together this is 260 liters of space for a processor that can make 200 liter batches.

Drainage: Since you will need to be able to drain glycerol, biodiesel, and maybe water out of your tank, drainage is an important part of any tank. Ideal is a tall skinny tank with a conical bottom and a valve on the very bottom for drainage. This is important because you want to make sure you can easily drain your glycerol wihtout draining (and thus wasting) your biodiesel as well. Having a drain that only partially dranks the tank or drains from the side (such as a hot water heater) can work for basic biodiesel processing, but can prevent many important processor addons later. It also will cause a build up of extremely dirty glycerol at the bottom of your tank which can make washing more difficult in the future.

Air Tightness: making your processor air tight is not necessary, but is advisable and very beneficial. Adding methoxide normally produces fumes which are extremely poisonous and explosive. Extremely good ventilation can help reduce these dangers, but having an airtight processor (most likely with a pressure release valve) eliminates the risk all together. For more information, read the Techniques and equipment for airtight processing section later in this chapter.

Integrating into your other needs Biodiesel processors have a number of other features. It is important to make sure that your tank has space and the ability to host these various features. These include: heaters, mixing devices, fume vents, insulation and a number of others. Metal tanks are often ideal because the fittings necessary for these parts can be welded on. HDPE tanks are often much more difficult to modify, but still possible. It is important to know what your processor needs before selecting a tank.

Common Tank Possibilities:

Hot Water Heaters: Hot water heaters are the standard for biodiesel processing in the US due to the ease in which they can be turned into biodiesel processors. They are air tight, have heaters built in, and can be easily plumbed to a pump for mixing. However, there are a few disadvantages. In many communities hot water heaters can't be found used and must be bought new and transported in. This cost can far outweigh their usefulness. Also, due to a glass lining that coats the inside of the tank, extra fittings are heavily discouraged from being added, which can prevent many later modifications. Lastly, hot water heaters don't drain completeley, leaving a small puddle of glycerol and contaminants which will constantly remain in the bottom of your processor.

55 gallon drums:

Are by far the easiest processing tanks for most to come by. They are generally much less expensive than hot water heaters and have more room for bigger batches. Because they are steel they can be modified in a number of ways. This includes welding conical bottoms for improved drainage, welding an assortment of fittings wherever the owner wants for increased mixing and heating options, and a variety of options regarding a top. The flipside of the coin is that the barrel requires modification to become a processor. Unlike a water heater, you dont simply attach the right parts and begin, at the least you must drill holes and add airtight seals. Generally you have to weld fittings for heaters and mixing ports, create a stand, and add insulation. This being said, the price for such welding and materials will still generally be far cheaper than a new hot water heater and better in the long run once built.

HDPE tanks Ease of modification?

5 gallon buckets:

Ideal if you don'tplan on making much biodiesel or want a cheap way to try processing biodiesel, 5 gallon buckets are a good way to go. This said, they are the least effecient of the tanks mentioned, and have a number of other restrictions. Generally, they have no bottom drainage and must be decanted, which is time consuming and the least effective way of seperating biodiesel from glycerol. Heating and mixing devices can both be plumbed into metal buckets (other options exist for plastic buckets) but for 3 gallon batches, this is generally not worth the cost. Most 5 gallon processors utilize a removable heater (Bucket heaters, which are difficult to find) and a stirring device of some kind through the lid.

Others:

The goal of this section is to give a resource for using not only standard tanks, but others as well. By reading through the rest of this chapter, and looking at some of the designs later on, you should be able to determine if a particular tank you have discovered would make a good processor or not. Possibilites worth investigating include: Large water tanks, propane tanks, and others.

-Curt Bowen